1. Field of the Invention
The present invention relates to a spin-valve type thin film magnetic element whose electric resistance changes in accordance to the relation between a fixed direction of magnetization of a fixed magnetic layer (pinned magnetic layer) and a direction of magnetization of a free magnetic layer being that are affected by an external magnetic field, and a thin film magnetic head comprising the spin-valve type thin film magnetic element. Particularly, the present invention relates to a technology suitable for use in a spin-valve type thin film magnetic element having an electrode layer comprising an overlay part extending on the surface of a laminated body from each side to the center of the laminated body.
2. Description of the Related Art
The spin-valve type thin film magnetic element is a kind of GMR (Giant Magnetic Electroresistive) element that senses recording magnetic fields from a recording medium such as a hard disk.
The spin-valve type thin film magnetic element has some excellent features such that it has a relatively simple structure among the GMR elements and a high rate of change of magnetoresistance against external magnetic fields, and the electrical resistance can be altered by a relatively weak magnetic field.
FIG. 24 shows a cross-sectional structure of one example of a conventional spin-valve type thin film magnetic element viewed from the face (ABS) side opposed to a recording medium.
The spin-valve type thin film magnetic element shown in FIG. 24 is a so-called bottom-type single spin-valve type thin film element in which one layer each of an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic conductive layer and a free magnetic layer are laminated.
The travel direction of the magnetic recording medium such as the hard disk is in the Z-direction, and the direction of leak magnetic field from the magnetic recording medium is in the Y-direction in this spin-valve type thin film magnetic element.
The conventional spin-valve type thin film magnetic element shown in FIG. 24 comprises a laminated body 109, a pair of hard bias layers 105 formed at both sides of the laminated body 109, and a pair of electrode layers 108 formed on the hard bias layers 105, wherein the laminated body 109 comprises, from the bottom to the top on a substrate, an underlayer 106, an antiferromagnetic layer 101, a pinned magnetic layer 102, a non-magnetic conductive layer 103, a free magnetic layer 104 and a protective layer 107. The electrode layer 108 comprises an overlay part 108a extending over the surface of the laminated body 109 from each side toward the center of the laminated body.
The underlayer 106 comprises Ta (tantalum), and the antiferromagnetic layer 101 is made of an alloy such as a NiCo alloy, a FeMn alloy and a NiMn alloy. The pinned magnetic layer 102 and free magnetic layer 104 is made of Co or a NiFe alloy, Cu is used for the non-magnetic conductive layer 103, the hard bias layer 105 is made of a Coxe2x80x94Pt (cobalt-platinum) alloy, and the electrode layer 108 is made of Cu.
An exchange coupling magnetic field (a coupling anisotropic magnetic field) is generated at the interface between the pinned magnetic layer 102 and antiferromagnetic layer 101, by forming the pinned magnetic layer 102 in contact with the antiferromagnetic layer 101. The direction of magnetization of the pinned magnetic layer 102 is fixed, for example, in the Y-direction.
The direction of variable magnetization of the free magnetic layer 104 is aligned in the X1-direction by magnetizing the hard bias layer 105 in the X1-direction. As a result, the direction of variable magnetization of the free magnetic layer 104 is made to be approximately perpendicular to the direction of magnetization of the pinned magnetic layer 102.
In this spin-valve type thin film magnetic element, a sense current flows from the electrode layer 108 formed on the hard bias layer 105 through the pinned magnetic layer 102, non-magnetic conductive layer 103 and free magnetic layer 104. The travel direction of the magnetic recording medium such as the hard disk is in the Z-direction, and the direction of magnetization of the free magnetic layer 104 changes from the X1-direction to the T-direction when a leak magnetic field from the magnetic recording medium is applied in the Y-direction. Electrical resistance changes in relation to directional changes of magnetization in the free magnetic layer 104 and in the pinned magnetic layer 102 (referred as magnetoresistive effect MR), and the leak magnetic field from the magnetic recording medium is sensed by utilizing the voltage changes based on this electrical resistance change.
As shown in FIG. 24, each electrode layer 108 has an overlay part 108a extending on the laminated body 109 in this spin-valve type thin film magnetic element. Accordingly, almost all the part of a sense current J flows into the laminated body 109 from the tip of the overlay part 108a of the electrode layer 108, when a sense current as a detection current is allowed to flow into the pinned magnetic layer 102, non-magnetic conductive layer 103 and free magnetic layer 104 from the electrode layer 108.
Consequently, a center part 104a, through which almost all the sense current J flows, and side parts (electrode overlay parts) 104, through which few sense current flows, are formed in the free magnetic layer 104.
The central part of the laminated body 109 located between the overlay parts 108a of each electrode layer 108 substantially contributes to regeneration of the recording magnetic field from the magnetic recording medium in this spin-valve type thin film magnetic element, and serves as a sensitive zone manifesting a magnetoresistive effect. Each side part of the laminated body 109 located at under each overlay part 108a serves as a dead zone that does not substantially contribute to regeneration of the recording magnetic field from the magnetic recording medium.
The sensitive zone and dead zone are thus provided by forming an overlay parts 108a of each electrode layer 108. The width of this sensitive zone corresponds to a track width Tw of the spin-valve type thin film magnetoresistive element. Consequently, the track width Tw can be narrowed by providing the overlay part 108a in each electrode layer 108, thereby enabling to comply with narrow track width for high density recording.
However, when the electrode layer 108 is thin and has high resistivity, or when the junction part between each electrode layer 108 and laminated body 109 has a large junction resistance, for example, the sense current J flowing from the overlay part 108a encounters large resistance, and the magnitude of a shunt current Jxe2x80x2 of the sense current J flowing in through the hard bias layer 105 turns out to be substantially large.
As a result, the sense current J flows through the region represented by symbols D in FIG. 24 that are located under each overlay part 108a of the laminated body 109. When the sense current J flows through the regions D that should be naturally the dead zones, voltage changes based on magnetoresistance changes against the external magnetic field appear in the region D, and signals in the recording track of the magnetoresistive recording medium corresponding to the region D is regenerated due to expressed voltage changes in the region D based on the magnetoresistance change against the external magnetic field.
In the case of the narrowing the tack width for attaining high density recording on the magnetic recording medium, in particular, a side-reading phenomenon occurs whereby a line of information on the adjoining magnetic recording track is read in the region D in place of another line of information on the magnetic recording track that should be naturally read in the sensitive zone. This side-reading phenomenon arises noises to the output signal, and may serve as error sources.
In addition to the problems as hitherto described, it has been a fundamental demand that output characteristics and sensitivity of the spin-valve type thin film magnetic element should be more improved.
Accordingly, it is an object of the present invention to provide a thin film magnetic head comprising a spin-valve type thin film magnetic element in which output characteristics are improved while preventing side-reading phenomena from occurring.
The present invention for solving the foregoing problems provides a spin valve type thin film magnetic element comprising a laminated body, a bias layer for aligning the direction of magnetization of the free magnetic layer to be approximately perpendicular to the direction of magnetization of the pinned magnetic layer, and an overlay part extending over the surface of the laminated body from each both side toward the center of the laminated body. The laminated body is formed by laminating, on a substrate, at least an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer in which the direction of magnetization is fixed by an exchange coupling magnetic field with the antiferromagnetic layer, and a free magnetic layer formed on the pinned magnetic layer by being separated with a non-magnetic conductive layer. The direction of magnetization of the free magnetic layer is aligned approximately in perpendicular to the direction of magnetization of the pinned magnetic layer. A pair of electrode layers for providing a sense current to the laminated body are further provided. In the spin-valve type thin film magnetic element according to the present invention, the relation represented by the following general equation is valid when the length vertically extending from an opposed face to an magnetic recording medium toward the inside of the magnetic element is represented by H1, a sheet resistance of the electrode layer is represented by Rs1, the length vertically extending from an opposed face to an magnetic recording medium toward the inside of the magnetic element, or the elevation of the element, is represented by Hg, and the sheet resistance of the laminated body is represented by Rsg:
(Rs1/H1)/(Rsg/Hg)xe2x89xa60.02
Since the spin-valve type thin film magnetic element as described above has the electrode layer comprising the overlay part extending on the surface of the laminated body from each side toward the center of the laminated body, the enter portion of the laminated body serves as a sensitive zone while each side portion located under the overlay part serves as a dead zone. Accordingly, the width of the sensitive zone may be used as a track width, enabling to comply with a narrow track width for high density recording.
In addition, since the relation of (Rs1/H1)/(Rsg/Hg)xe2x89xa60.02 is valid when the length vertically extending from an opposed face to an magnetic recording medium toward the inside of the magnetic element is represented by H1, a sheet resistance of the electrode layer is represented by Rs1, the length vertically extending from an opposed face to an magnetic recording medium toward the inside of the magnetic element, or the elevation of the magnetic element, is expressed by Hg, and the sheet resistance of the laminated body is expressed by Rsg, the resistance against a sense current flowing in from the overlay part may be reduced, thereby also reducing a shunt sense current flowing in through the bias layer. As a result, the sense current flowing in the dead zone located at under the overlay part of the laminated body is reduced to prevent voltage changes in the dead zone from occurring. Consequently, side-reading of the spin-valve type thin film magnetic element may be also prevented.
Reducing the shunt sense current, and converging the sense current on the sensitive zone located at the center of the laminated body allow voltage changes in the sensitive region to be improved, thereby enabling output characteristics of the spin-valve type thin film magnetic element to be improved.
The range of the sensitive zone of the laminated body may be determined by a micro-track profile method.
This means that the xe2x80x9csensitive zonexe2x80x9d can be defined as a zone where a signal with an intensity of 50% or more of the maximum signal intensity is obtained among the regenerative signals obtained by scanning the spin-valve type thin film magnetic element on a micro-track on which signals have been recorded.
The xe2x80x9cdead zonexe2x80x9d of the laminated body is located at each side of the sensitive zone, and can be defined as a zone where the signal intensity is reduced to 50% or less of the maximum signal intensity.
Preferably, H1, Rs1, Hg and Rsg satisfy the relation represented by the following general equation in the spin-valve type thin film magnetic element described above:
(Rs1/H1)/(Rsg/Hg)xe2x89xa60.01
The electrical resistance against the sense current flowing in from the overlay part may be more reduced, thereby further reducing the sense current flowing in through the bias layer, by providing a spin-valve type thin film magnetic element satisfying the equation above.
Consequently, side-reading of the spin-valve type thin film magnetic element may be more effectively prevented. It is also possible to further improve output characteristics of the spin-valve type thin film magnetic element by enhancing voltage changes in the sensitive zone.
The present invention also provides a spin valve type thin film magnetic element comprising a laminated body, a bias layer for aligning the direction of magnetization of the free magnetic layer to be approximately perpendicular to the direction of magnetization of the pinned magnetic layer, and an overlay part extending over the surface of the laminated body from the each side toward the center of the laminated body. The laminated body is formed by laminating, on a substrate, at least an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer in which the direction of magnetization is fixed by an exchange coupling magnetic field with the antiferromagnetic layer, and a free magnetic layer formed on the pinned magnetic layer by being separated with a non-magnetic conductive layer. The direction of magnetization of the free magnetic layer is aligned to be approximately perpendicular to the direction of magnetization of the pinned magnetic layer. A pair of electrode layers for providing a sense current to the laminated body are further provided. The relation represented by the following general equation is valid when the length vertically extending from an opposed face to an magnetic recording medium toward the inside of the electrode layer is represented by H1, the length Hg vertically extending from an opposed face to an magnetic recording medium toward the inside of the laminated body, or the elevation of the element, is adjusted in the range of 0.2 to 0.5 xcexcm, and a sheet resistance Rsg of the electrode layer is adjusted in the range of 15 to 25 xcexa9/M2:
(Rs1/H1)/(Rsg/Hg)xe2x89xa61 xcexa9/xcexcm
The electrical resistance against the sense current flowing in from the overlay part may be reduced, thereby enabling a shunt sense current flowing in through the bias layer to be reduced, in the spin-valve type thin film magnetic element so constructed as described above. As a result, the sense current flowing in the dead zone located under the overlay part of the laminated body may be reduced to prevent voltage changes in the dead zone from appearing, thereby enabling side reading of the spin-valve type thin film magnetic element to be prevented.
Since the shunt sense current is reduced to enable the sense current to be converged on the sensitive zone located at the center of the laminated body, and voltage changes at the sensitive zone may be enhanced to enable output characteristics of the spin-valve type thin film magnetic element to be improved.
Desirably, the relation represented by the following general equation is valid in the relation between H1 and Rs1 when Hg is adjusted within the range of 0.2 to 0.5 xcexcm and Rsg is adjusted within the range of 15 to 25 xcexa9/M2:
(Rs1/H1)xe2x89xa60.5 xcexa9/xcexcm
The electrical resistance against the sense current flowing in from the overlay part may be reduced, thereby enabling a shunt sense current flowing in through the bias layer to be reduced, in the spin-valve type thin film magnetic element so constructed as described above.
As a result, side reading of the spin-valve type thin film magnetic element may be more effectively prevented. Voltage changes in the sensitive zone is further enhanced to enable output characteristics of the spin-valve type thin film element to be more improved.
Desirably, the angle formed between the surface of the overlay part of the electrode layer and the surface of the laminated body is within the range of 45 degrees to 70 degrees in the spin-valve type thin film magnetic element as hitherto described.
The electrical resistance against the sense current flowing in from the overlay part may be reduced, thereby enabling a shunt sense current flowing in through the bias layer to be reduced, in the spin-valve type thin film magnetic element so constructed as described above.
Reducing the shunt current allows side reading of the spin-valve type thin film magnetic element to be more effectively prevented. Output characteristics of the spin-valve type thin film element may be also more improved as a result of enhancing voltage changes in the sensitive zone.
The spin-valve type thin film magnetic element as described above may comprise a dual structure in which the non-magnetic conductive layer, pinned magnetic layer and antiferromagnetic layer are formed on both side of the free magnetic layer, respectively, in the direction of thickness.
Two sets of combinations of the three layers of the free magnetic layer/non-magnetic conductive layer/pinned magnetic layer are available in the spin-valve type thin film magnetic element as described above, which may provide a larger rate of change of magnetoresistance (xcex94R/R) as compared with a single spin-valve type thin film magnetic element to make it possible to comply with high recording density of the magnetic head.
Desirably, the spin-valve type thin film magnetic element comprises a mean free path extension layer for extending the mean free path of conduction electrons.
The xe2x80x9cmean free path extension layerxe2x80x9d as used herein refers to at least one of a backed layer and a specular layer.
In the spin-valve type thin film magnetic element as described above, the mean free path of the conduction electrons having (+)-spins (up-spin) that are responsible for the magnetoresistive effect may be extended to obtain a so-called spin-filter effect, thereby obtaining a large rate of change of magnetoresistance (xcex94R/R) to comply with high density recording of the magnetic head.
Providing a specular layer as the mean free path extension layer in the spin-valve type thin film magnetic element described above allows the rate of change of magnetoresistance to be increased by a specular effect as will be described hereinafter.
The reason why the rate of change of magnetoresistance increases by providing the backed layer and specular layer will be described below. Before the description, the principle of a giant magnetoresistive effect in the spin-valve type thin film magnetic element will be briefly described. An example when the backed layer or the specular layer is disposed at a position where the free magnetic layer does not contact the non-magnetic conductive layer will be described herein.
The conduction electrons mainly travels in the vicinity of the non-magnetic conductive layer having a smaller electrical resistance when a sense current is applied to the spin-valve type thin film magnetic element. The conduction electrons involve two kinds of conduction electrons having up-spins ((+)-spins or upward spins) and down-spins ((xe2x88x92)-spins or downward spins) in equal probability.
The rate of change of magnetoresistance of the spin-valve type thin film magnetic element is positively correlated with the mean free path of these two kinds of conduction electrons.
The conduction electrons having down-spins are always scattered at the interface between the non-magnetic conductive layer and free magnetic layer irrespective of the direction of the applied external magnetic field, and the probability for allowing the conduction electrons to be transferred to the free magnetic layer remains low. Accordingly, the mean free path of the down-spin electrons remains shorter as compared with the up-spin conduction electrons.
The conduction electrons having up-spins are transferred from the non-magnetic conductive layer to the free magnetic layer with a high probability, when the direction of magnetization of the free magnetic layer turn out to be in parallel relation to the direction of magnetization of the pinned magnetic layer, thereby making the mean free path of the conduction electrons longer. The mean free path is shortened, on the other hand, as a result of high incidence of scattering at the interface between the non-magnetic conductive layer and free magnetic layer, as the direction of magnetization of the free magnetic layer shifts from the parallel direction when the direction of magnetization of the pinned magnetic layer is affected by the external magnetic field.
The mean free path of the up-spin conduction electrons is greatly changed by the action of the external magnetic field, as compared with the mean free path of the down-spin conduction electrons. Large change in the free path differences of the mean free path among the up-spin conduction electrons results in resistivity changes, also increasing the rate of change of magnetoresistance (xcex94R/R) of the spin-valve type thin film magnetic element.
Connecting the backed layer to the free magnetic layer enables the up-spin conduction electrons traveling in the free magnetic layer to be transferred into the backed layer, and the mean free path of the up-spin conduction electrons may be further extended in proportion to the thickness of the backed layer. Consequently, a so-called spin-filter effect may be manifested to increase the mean free path differences of the conduction electrons, thereby enabling the rate of change of magnetoresistance (xcex94R/R) of the spin-valve type thin film magnetic element to be further improved.
When the specular layer is laminated on the position where the free magnetic layer does not contact the non-magnetic conductive layer, on the other hand, a potential barrier is formed at the interface between the specular layer and free magnetic layer. As a result, the up-spin conduction electrons traveling in the free magnetic layer may be reflected while their spin states conserved, thereby enabling specular reflection of the up-spin conduction electrons. Accordingly, the mean free path of the up-spin conduction electrons may be extended. The so-called specular effect may be expressed as a result of extended mean free path, and the mean free path differences among the spin-dependent conduction electrons are further increased to enhance the rate of change of magnetoresistance of the spin-valve type thin film magnetic element.
When a specular layer is laminated at the opposite side to the face of the backed layer, which is connected to the free magnetic layer and in contact with the free magnetic layer, the mean free path of the up-spin conduction electrons increases by the spin-filter effect, and the so-called specular effect may be expressed due to the potential barrier formed at the interface between the specular layer and backed layer. Consequently, the mean free path of the up-spin conduction electrons may be further extended by allowing the up-spin conduction electrons to be reflected while conserving their spin states. The mean free path differences among the spin-dependent conduction electrons are further increased to enhance the rate of change of magnetoresistance of the spin-valve type thin film magnetic element.
At least one of the pinned magnetic layer and free magnetic layer may be divided in two parts by being separated with the non-magnetic intermediate layer, and the direction of magnetization of one of the divided layer is by 180xc2x0 different from the direction of magnetization of the other divided layer to form a ferrimagnetic state in the spin-valve type thin film magnetic element as hitherto described.
When at least the pinned magnetic layer is divided in two parts by being separated with the non-magnetic intermediate layer in the spin-valve type thin film magnetic element, one of the divided pinned magnetic layers serves for fixing the direction of magnetization of the other divided pinned magnetic layer in a proper direction, thereby enabling the magnetic state of the pinned magnetic layer to be maintained in a quite stable state.
An exchange coupling magnetic field is generated, on the other hand, between the divided free magnetic layers, when at least the free magnetic layer is divided into two layers by being separated with the non-magnetic intermediate layer. The free magnetic layers are put into a ferrimagnetic state to permit magnetization of the free magnetic layer to be sensitively reversed against the external magnetic field.
Desirably, the antiferromagnetic layer comprises an alloy containing Mn, and at least one element of Pt, Pd, Rh, Ru, Ir, Os, Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr in the spin-valve type thin film magnetic element as hitherto described.
The antiferromagnetic layer comprising the alloy as described above has a high exchange coupling magnetic field, is excellent in corrosion resistance, and can express a sufficient exchange coupling magnetic field even at a relatively high temperature. Therefore, the operation of the spin-valve type thin film magnetic element may be stabilized particularly even at a relatively high temperature.
The problems as hitherto described can be solved by the thin film magnetic head comprising the spin-valve type thin film magnetic element as described above.
Since the thin film magnetic head comprises the spin-valve type thin film magnetic element as hitherto described, it may be used as a thin film magnetic head having a high regenerative output of magnetic information while having a low incidence of side reading.